Description: (Taken directly from the application) The aim of this Core is to develop transgenic mouse strains either by pronuclear injection of DNA or by blastocyst injection of genetically modified embryonic stem (ES) cells. These procedures not only require considerable skill they require dedicated equipment and facilities. The Core will facilitate genetic approaches which underpin each of the projects in this program. It will facilitate in training individuals from member laboratories who are unfamiliar with these procedures.